docs: def get_namespace(self, name_seq):
          """Returns the prefix of names from name_seq that are known namespaces.
  
          Args:
            name_seq: ['names', 'of', 'possible', 'namespace', 'to', 'find']
  
          Returns:
            ['names', 'that', 'are', 'namespaces', 'possibly', 'empty', 'list']
          """
          namespaces = self.namespaces
          result = []
          for name in name_seq:
              namespaces = namespaces.get(name)
              if not namespaces:
                  break
              result.append(name)
          return result